The eporeodon was exhausted. She staggered toward the stream, her thirst compelling her trembling legs. Her zebra-like stripes were stained with clay where she had fallen. The ancient relative of pigs and camels was confused and fearful. The shaking of the earth had disoriented her and disturbed her habits. She had been unable to grasp more than a mouthful of grass here and there and was ready to collapse. She had run in terror as the first rumble shook the ground under her feet and the terror had continued without pause for three days. She could no longer run. Her strength was gone and even the drive of her extreme thirst could muster no more than a shuffling walk.
As she neared the edge of the water, a particularly violent rumble shook her off her unsteady feet and she tumbled into the stream. It was scalding hot and her feeble cries of pain were drowned in the blast that shook the foundations of the stream. The roar of the blast was the last sound she would hear.
Far below, 300 miles within the earth, the impact of the Farallon and North American tectonic plates had been changing. Orthogonal compression had changed to oblique strike slip and the Farallon plate began to melt in the mantle as it subducted beneath the North American plate.
The water-rich clay and sediment at the top of the Farallon plate produced large quantities of water as the basalt rocks were transformed into eclogite and the pressure and heat began to rise. At temperatures of more than 700 degrees F and pressures of more than 3500 psi, the water passed its critical point and formed super-critical fluids, blurring the distinction between liquids and gases.
The fluid sought release and began to dissolve the overriding plate. The magma, forced into the cavities left by the ascending fluids, exploded upward under the tremendous pressures. The rock of the plate began to melt and the boundary between the plates became an inferno.
At the surface, the seismic activity reached a climax and the single loudest noise in history split the heavens. The titanic explosion took little notice of the death of one small eporeodon.
The giant in the earth had slumbered for 30 million years. Its heart thudded slowly and the weight of batholithic tons rested upon its eyelids. Something stirred in the depths and a shudder moved through sluggish nerves. The giant sensed an intolerable weight resting upon its shoulders. Its feet reached down and found purchase. Sensing the crystallized coldness of its prison, it raised its visage toward the freedom of heaven and roared. Above, the ancient walls of its prison began to flow, and heat, borne up through the slow bloodstreams, began to flow. The giant was awake, and its fury, so long imprisoned, was ready to be unleashed. It flexed its shoulders and discovered it was strong.
Near Parkfield, California, in the creeping section of the San Andreas Fault, seismic tension had been building to intolerable levels. A sudden slip along the margin of the Pacific Plate set seismic vibrations rumbling along the fault. It was not a large quake, 4.2 on the scale, but those living along the fault definitely felt it. The unfelt portions were more dramatic. Deep beneath the Great Valley, the remnants of the Farallon Slab known as the Isabella Anomaly had lain sleeping. An irregularity in the bottom surface of the crust had caused it to break off the primary slab and it had been frozen in time for millennia, creeping a few inches in a thousand years. The vibration from the seismic event caused a tear along the irregularity and it was free. The subduction interface, dormant for millennia, slipped and began to move eastward and downward into the mantle. It began to melt. Magma was on the move, seeking the ancient channels and thrusting its way toward the surface and freedom. The lower crust, already very thin in the plate gap, softened as it melted.